The present invention relates to a vehicular height adjustment control mechanism. More particularly, the present invention relates to an improved height adjustment control mechanism for farm implement platforms or running gear having at least two wheels or ground contact points and that are towed behind a powered vehicle.
Large scale, mechanized agriculture today utilizes many power-driven assemblies of tools and cultivation implements to accomplish the objectives of cultivating and planting fields faster, more efficiently, and with less expenditure of resources. To this end, tractors, combines, and other machines capable of preparing, planting and harvesting large areas have been developed to meet the needs of modern farming. A mainstay of today's agriculture is the tool-carrying platform or running gear that is towed behind a powered vehicle such as a tractor. These farm implement platforms perform many tasks in the field, and it is important that they perform in a flexible yet consistent manner. A key to dependable performance of a platform is maintaining the height at which it traverses the often times uneven and rough surface of a field. If the platform crosses the field parallel to the field's surface, the tools that extend from the platform into the ground will maintain a desired, preset depth of penetration into the earth. This is an important factor in planting because seed depth, for example, determines, in part, when the plants will germinate and subsequently grow. If a crop is late due to being planted too deeply, it may be mature late. This, in turn, exposes the crop to more severe and unpredictable weather.
Various methods and mechanisms have been utilized in the past in an attempt to maintain the attitude of a farm implement platform as it is towed across rough ground. Probably the most basic of all mechanisms incorporates manual adjustment of the platform height. To adjust platform height, the tractor is stopped, and the operator would physically adjust the elevation of the platform. A disadvantage of the manually-adjustable platform is its inability to be easily adjusted without stopping the platform and tractor for significant amounts of time.
Another means commonly used to vary and/or maintain the height of a farm implement platform is through utilization of pneumatic or hydraulic controls and cylinders. (In this application, "hydraulics" as a term shall encompass both air and oil controls and cylinders.) Such means typically necessitate a complex array of pumps, hoses, fluids, valves and cylinders to transmit power and adjust platform attitude. A disadvantage that stems from the very nature of a hydraulic system is its tendency to leak fluid. Movement of mechanical components is attained by applying pressurized fluid to a piston located within a cylinder. The seals required to separate the pressurized hydraulic fluid from the atmosphere wear, and leaks occur. Also, hoses used to interconnect various hydraulic components may crack under extremes of pressure. Constantly changing pressure within the hydraulic system, such as is experienced when encountering rough terrain, stresses the mechanical components, increases the likelihood of leaks developing at joints, and increases the likelihood of hoses developing cracks.
U.S. Pat. No. 3,658,362 (Fackler, et al.) discloses a hydraulic cylinder construction that rotates an axle upon which the wheels are mounted. Extension of the cylinder rod by pressurizing the cylinder moves the wheels down relative to the platform, thus raising the platform. A potential disadvantage of the Fackler system is that the hydraulic cylinder may need to be kept pressurized in order to maintain the desired platform height. This may cause excessive wear of hydraulic components, because constantly changing pressure in the hydraulic system, which occurs when the platform encounters bumps or dips in the ground, can cause faster wear than is preferred. Therefore, some manner of extending the lifetime of a hydraulic system is desired. To this end, some means for relieving pressure on hydraulic hoses and cylinders may extend the life of the hydraulic system.
Another disadvantage of constant-pressure hydraulic systems is that of the crippling effect that occurs when there is a failure of the hydraulics. If a leak develops or the hydraulic fluid level becomes too low, no pressure can be maintained. The system loses its ability to maintain or change its prior position.